package com.ciwong.epaper.modules.epaper.util;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PushbackInputStream;
import java.io.Reader;

/**
 * 读取带BOM的UTF-8格式文件 Created by pla-gysu on 2015/8/5.
 */
public class UnicodeReader extends Reader
{

    PushbackInputStream internalIn;

    InputStreamReader internalIn2 = null;

    String defaultEnc;

    private static final int BOM_SIZE = 4;

    /**
     *
     * @param in
     *            inputstream to be read
     * @param defaultEnc
     *            default encoding if stream does not have BOM marker. Give NULL
     *            to use system-level default.
     */
    public UnicodeReader(InputStream in, String defaultEnc)
    {
        internalIn = new PushbackInputStream(in, BOM_SIZE);
        this.defaultEnc = defaultEnc;
    }

    public String getDefaultEncoding()
    {
        return defaultEnc;
    }

    /**
     * Get stream encoding or NULL if stream is uninitialized. Call init() or
     * read() method to initialize it.
     */
    public String getEncoding()
    {
        if (internalIn2 == null)
            return null;
        return internalIn2.getEncoding();
    }

    /**
     * Read-ahead four bytes and check for BOM marks. Extra bytes are unread
     * back to the stream, only BOM bytes are skipped.
     */
    protected void init() throws IOException
    {
        if (internalIn2 != null)
            return;

        String encoding;
        byte bom[] = new byte[BOM_SIZE];
        int n, unread;
        n = internalIn.read(bom, 0, bom.length);

        if ((bom[0] == (byte) 0x00) && (bom[1] == (byte) 0x00)
                && (bom[2] == (byte) 0xFE) && (bom[3] == (byte) 0xFF))
        {
            encoding = "UTF-32BE";
            unread = n - 4;
        }
        else if ((bom[0] == (byte) 0xFF) && (bom[1] == (byte) 0xFE)
                && (bom[2] == (byte) 0x00) && (bom[3] == (byte) 0x00))
        {
            encoding = "UTF-32LE";
            unread = n - 4;
        }
        else if ((bom[0] == (byte) 0xEF) && (bom[1] == (byte) 0xBB)
                && (bom[2] == (byte) 0xBF))
        {
            encoding = "UTF-8";
            unread = n - 3;
        }
        else if ((bom[0] == (byte) 0xFE) && (bom[1] == (byte) 0xFF))
        {
            encoding = "UTF-16BE";
            unread = n - 2;
        }
        else if ((bom[0] == (byte) 0xFF) && (bom[1] == (byte) 0xFE))
        {
            encoding = "UTF-16LE";
            unread = n - 2;
        }
        else
        {
            // Unicode BOM mark not found, unread all bytes
            encoding = defaultEnc;
            unread = n;
        }
        // System.out.println("read=" + n + ", unread=" + unread);

        if (unread > 0)
            internalIn.unread(bom, (n - unread), unread);

        // Use given encoding
        if (encoding == null)
        {
            internalIn2 = new InputStreamReader(internalIn);
        }
        else
        {
            internalIn2 = new InputStreamReader(internalIn, encoding);
        }
    }

    public void close() throws IOException
    {
        init();
        internalIn2.close();
    }

    public int read(char[] cbuf, int off, int len) throws IOException
    {
        init();
        return internalIn2.read(cbuf, off, len);
    }

}
